U.S. patent application number 14/992377 was filed with the patent office on 2016-09-29 for inclination detection method, inclination detection apparatus, and equipment for detecting inclination.
This patent application is currently assigned to HITACHI, LTD.. The applicant listed for this patent is HITACHI, LTD.. Invention is credited to Tadaaki Ishikawa.
Application Number | 20160280036 14/992377 |
Document ID | / |
Family ID | 56973920 |
Filed Date | 2016-09-29 |
United States Patent
Application |
20160280036 |
Kind Code |
A1 |
Ishikawa; Tadaaki |
September 29, 2016 |
INCLINATION DETECTION METHOD, INCLINATION DETECTION APPARATUS, AND
EQUIPMENT FOR DETECTING INCLINATION
Abstract
An inclination detection apparatus detects the inclination of a
mobile body with three marker rods having different inclinations
with respect to one another. The mobile body is provided with a
laser range finder irradiating surrounding objects with a laser
beam to light a point on each of the three marker rods as a
reflection point from which the laser beam is reflected back. The
inclination detection apparatus includes a processor and a storage
device storing relative positional information of the three marker
rods. The processor obtains positional information of reflection
points, obtains relative positions of the reflection points on the
three marker rods by determining points on the three marker rods
corresponding to the obtained positional information based on the
relative positional information of the three marker rods, and
identifies an inclination plane including the obtained relative
positions of the reflection points as the inclination of the mobile
body.
Inventors: |
Ishikawa; Tadaaki; (Tokyo,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
HITACHI, LTD. |
Tokyo |
|
JP |
|
|
Assignee: |
HITACHI, LTD.
Tokyo
JP
|
Family ID: |
56973920 |
Appl. No.: |
14/992377 |
Filed: |
January 11, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G01C 2009/066 20130101;
G01C 9/06 20130101; B60G 17/01908 20130101; G05D 1/0891 20130101;
G05D 2201/0216 20130101; G05D 1/0236 20130101 |
International
Class: |
B60G 17/019 20060101
B60G017/019; G05D 1/00 20060101 G05D001/00; G01C 9/06 20060101
G01C009/06 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 26, 2015 |
JP |
2015-064575 |
Claims
1. A method for detecting an inclination of a mobile body using an
inclination detection apparatus having a processor and a storage
device with three marker rods having different inclinations with
respect to one another, the storage device storing relative
positional information of the three marker rods, the mobile body
being provided with a laser range finder irradiating surrounding
objects with a laser beam to light a point on each of the three
marker rods as a reflection point from which the laser beam is
reflected back to the laser range finder, the method being carried
out by the processor and comprising the steps of: obtaining
positional information of reflection points of the laser beam,
obtaining relative positions of the reflection points on the three
marker rods by determining points on the three marker rods
corresponding to the obtained positional information of the
reflection points based on the relative positional information of
the three marker rods, and identifying an inclination plane
including the obtained relative positions of the reflection points
as the inclination of the mobile body.
2. The method set forth in claim 1, wherein the three marker rods
having different inclinations with respect to one another are
skewed with respect to one another.
3. The method set forth in claim 1, the method further comprising
sending a control signal to a controller controlling an inclination
of the whole of the mobile body, the control signal commanding the
controller to change the inclination of the whole of the mobile
body in such a manner as to restore the inclination plane to a
level position.
4. The method set forth in claim 2, the method further comprising
sending a control signal to a controller controlling an inclination
of the whole of the mobile body, the control signal commanding the
controller to change the inclination of the whole of the mobile
body in such a manner as to restore the inclination plane to a
level position.
5. The method set forth in claim 1, wherein the mobile body is
further provided with a loading platform on which an article to be
transferred is to be loaded, the method further comprising sending
a control signal to a controller controlling an inclination of the
loading platform, the control signal commanding the controller to
change the inclination of the loading platform in such a manner as
to restore the inclination plane to a level position.
6. The method set forth in claim 2, wherein the mobile body is
further provided with a loading platform on which an article to be
transferred is to be loaded, the method further comprising sending
a control signal to a controller controlling an inclination of the
loading platform, the control signal commanding the controller to
change the inclination of the loading platform in such a manner as
to restore the inclination plane to a level position.
7. An inclination detection apparatus for detecting an inclination
of a mobile body with three marker rods having different
inclinations with respect to one another, the mobile body being
provided with a laser range finder irradiating surrounding objects
with a laser beam to light a point on each of the three marker rods
as a reflection point from which the laser beam is reflected back
to the laser range finder, the inclination detection apparatus
comprising: a storage device storing relative positional
information of the three marker rods, and a processor configured
to: obtain positional information of reflection points of the laser
beam, obtain relative positions of the reflection points on the
three marker rods by determining points on the three marker rods
corresponding to the obtained positional information based on the
relative positional information of the three marker rods, and
identify an inclination plane including the obtained relative
positions of the reflection points as the inclination of the mobile
body.
8. The inclination detection apparatus set forth in claim 7,
wherein the three marker rods having different inclinations with
respect to one another are skewed with respect to one another.
9. The inclination detection apparatus set forth in claim 7,
wherein the processor is further configured to send a control
signal to a controller controlling an inclination of the whole of
the mobile body, the control signal commanding the controller to
change the inclination of the whole of the mobile body in such a
manner as to restore the inclination plane to a level position.
10. The inclination detection apparatus set forth in claim 8,
wherein the processor is further configured to send a control
signal to a controller controlling an inclination of the whole of
the mobile body, the control signal commanding the controller to
change the inclination of the whole of the mobile body in such a
manner as to restore the inclination plane to a level position.
11. The inclination detection apparatus set forth in claim 7,
wherein the mobile body is further provided with a loading platform
on which an article to be transferred is to be loaded, and wherein
the processor is further configured to send a control signal to a
controller controlling an inclination of the loading platform, the
control signal commanding the controller to change an inclination
of the loading platform in such a manner as to restore the
inclination plane to a level position.
12. The inclination detection apparatus set forth in claim 8,
wherein the mobile body is further provided with a loading platform
on which an article to be transferred is to be loaded, and wherein
the processor is further configured to send a control signal to a
controller controlling an inclination of the loading platform, the
control signal commanding the controller to change an inclination
of the loading platform in such a manner as to restore the
inclination plane to a level position.
13. Equipment for detecting an inclination, the equipment
comprising three maker rods whose relative positions are fixed,
wherein each of the three marker rods is to be irradiated by a
laser range finder with a laser beam which is to be reflected on a
reflection point on the marker rod, and thereby to make the laser
beam finder measure relative positions of the reflection points of
the three marker rods with respect to the laser beam finder.
14. The equipment for detecting an inclination set forth in claim
13, wherein each of the marker rods is applied thereon with a
retroreflective material for reflecting the laser beam.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to an inclination detection
method, an inclination detection apparatus, and equipment for
detecting inclination.
DESCRIPTION OF THE PRIOR ART
[0002] In large-scale factories, warehouses serving as a transfer
point in physical distribution, and hospitals needing provision of
meals as well as collection and distribution of laundry, automated
guided vehicles and mobile robots having a transfer function are
common for the purpose of labor-saving in article transfer. These
unmanned transfer vehicles transfer articles with the articles
being carried directly on the vehicle, or put in a shelf, a tray,
or a container, which is carried on the vehicle.
[0003] When an unmanned transfer vehicle is in automatic operation,
it is necessary to make the vehicle recognize the position of the
vehicle itself. Many unmanned transfer vehicles have been
configured to determine individual positions of the vehicles
themselves by utilizing white line markers, barcode markers,
magnetic markers, RFID tags, and the like installed on a floor
surface as markers for position recognition. However, the position
recognition of unmanned vehicles nowadays are conducted often with
a guidance system using a laser range finder (LRF) fixed on an
unmanned transfer vehicle and map information, in consideration
that it takes a lot of time and effort to accurately install
markers on predetermined positions and that the markers installed
on a floor surface are likely to become unusable due to a breakage
of or stain on the marker.
[0004] A general two-dimensional LRF emits laser beams around the
LRF in such a manner as to scan a plane and measures distance to an
object based on the time for the laser beam to light the object and
return to the LRF as reflection light, and thus the detection plane
of such an LRF forms a two dimensional place. The unmanned transfer
vehicle then compares the two-dimensional positional information of
surrounding objects obtained by the LRF with a map prepared in
advance, determines the position of the vehicle itself, and travels
according to a preset route-following program.
[0005] A surrounding object the distance to which is to be measured
can be anything as long as the laser beam spot on that object can
be detected by a photodetector of the LRF. For example, a wall, a
pillar, or a casing of an installed apparatus can be used as is.
Some type of LRF measures a distance based on the positions of a
photoemitter and a photodetector by means of the triangulation
principle. The detection plane of such an LRF also forms a two
dimensional plane.
[0006] When an unmanned transfer vehicle is in automatic operation,
it is necessary to make the vehicle recognize the inclination of
the vehicle itself. Due to improved performance of unmanned
transfer vehicles and evolution in physical distribution systems,
there has been an increasing demand for unmanned transfer vehicles
to transfer heavy articles and tall articles such as a shelf. To
transfer an article safely or accurately, it is necessary for an
unmanned transfer vehicle to recognize the inclination of the
vehicle itself on which an article to be transferred has been
loaded.
[0007] Examples of means for recognizing the inclination of an
unmanned transfer vehicle include a general tiltmeter and a general
giro, which utilize gravity. However, integration of such a
measurement device into a transfer vehicle will cause problems
concerning cost and maintenance. Hence, Japanese Unexamined Patent
Application Publication No. 2001-075645 (patent literature 1)
proposes a method for measuring the inclination of a vehicle body
by utilizing an LRF.
[0008] The layout of a warehouse, in which operation routes on
which unmanned transfer vehicles travel are to be defined, is often
altered for example due to changes in the stock status of the
warehouse. Thus, for the purpose of following layout changes, it is
desirable to save time and effort for preparing preliminary
information for calculating the inclination of unmanned transfer
vehicles.
[0009] Unfortunately, the method of the patent literature 1
requires that positional information of retroreflectors, which are
to reflect the laser beam from an LRF, be input in advance per each
retroreflector, and thus moving retroreflectors according to a
layout change requires significant time and effort for inputting
the positional information of the retroreflectors again.
SUMMARY OF THE INVENTION
[0010] In view of the above, a major object of the present
invention is to detect the inclination of a mobile body in such a
manner that it is possible to flexibly support changes made in the
travel route of the mobile body.
[0011] In order to solve the above problem, an aspect of the
present invention provides an inclination detection apparatus for
detecting an inclination of a mobile body with three marker rods
having different inclinations with respect to one another. The
mobile body is provided with a laser range finder. The laser range
finder irradiates surrounding objects with a laser beam to light a
point on each of the three marker rods as a reflection point from
which the laser beam is reflected back to the laser range finder.
The inclination detection apparatus includes a storage device and a
processor. The storage device stores relative positional
information of the three marker rods. The processor is configured
to: obtain positional information of reflection points, obtain
relative positions of the reflection points on the three marker
rods by determining points on the three marker rods corresponding
to the obtained positional information based on the relative
positional information of the three marker rods, and identify an
inclination plane including the obtained relative positions of the
reflection points as the inclination of the mobile body.
[0012] Other aspects of the invention will be explained below in
the embodiments embodying the invention.
[0013] According to the present invention, the inclination of a
mobile body can be detected in such a manner that it is possible to
flexibly support changes in the route of the mobile body.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIGS. 1A to 1C are views showing that, in an embodiment of
the invention, a transfer vehicle on which an article to be
transferred has been loaded irradiates a marker with a laser beam,
where FIG. 1A is a perspective view; FIG. 1B is a plan view as
viewed directly from the top of the transfer vehicle; and FIG. 1C
is a side view as viewed directly from a side of the transfer
vehicle.
[0015] FIG. 2 is a flowchart showing a process of the transfer
vehicle to travel, which process includes an inclination detection
process by an inclination detection apparatus according to the
embodiment of the invention.
[0016] FIGS. 3A to 3C are explanatory diagrams for explaining an
inclination detection process according to the embodiment of the
invention, where FIG. 3A is an explanatory diagram for explaining a
process of detecting the reflection points of the laser beam
relative to an LRF; FIG. 3B is an explanatory diagram for
explaining a process of forming a triangle from the positions of
the reflection points detected in the process explained with FIG.
3A, to obtain the lengths of the sides of the triangle; and FIG. 3C
is an explanatory diagram showing that an inclination plane is
obtained by determining points on marker rods of a maker which form
a triangle having the same lengths of sides as the lengths of the
sides of the triangle obtained in the process explained with FIG.
3B.
[0017] FIGS. 4A to 4C are schematic diagrams showing examples of
the inclination plane to be detected by the embodiment of the
invention, where FIG. 4A shows an inclination plane formed when the
transfer vehicle has an inclination with a front portion of the
transfer vehicle being raised (bends oneself back); FIG. 4B shows
an inclination plane formed when the transfer vehicle has an
inclination with the front portion of the transfer vehicle being
lowered (bends oneself forward); and FIG. 4C shows an inclination
plane formed when the transfer vehicle goes up a slope.
[0018] FIGS. 5A and 5B are views for explaining how an article to
be transferred is restored to its level position according to an
embodiment of the invention, where FIG. 5A is a plan view
illustrating an inclined transfer vehicle with an article loaded on
a loading platform of the vehicle; FIG. 5B is a plan view
illustrating that the article has been restored to its level
position by adjusting the loading platform. FIGS. 5C and 5D are
views for explaining how an article to be transferred is restored
to its level position according to an embodiment of the invention,
where FIG. 5C is a plan view illustrating an inclined transfer
vehicle provided with actuators between the vehicle body and wheel
shafts; FIG. 5D is a plan view illustrating that the whole of the
vehicle has been restored to its level position by adjusting the
actuators.
[0019] FIG. 6A is a perspective view illustrating an embodiment of
the invention which is different from the embodiment illustrated in
FIG. 1A. FIG. 6B is a perspective view illustrating embodiments of
the marker which are different from the marker illustrated in FIG.
1A.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0020] An embodiment of the present invention will now be described
in detail with reference to the accompanying drawings.
[0021] FIG. 1A is a perspective view showing that a transfer
vehicle 2 on which an article 3 to be transferred has been loaded
irradiates a marker (equipment for detecting an inclination) with a
laser beam 22;
[0022] The transfer vehicle 2 is a mobile body such as an unmanned
transfer vehicle or a mobile robot which is used for transferring
articles for example in a factory, a warehouse, or a hospital. The
transfer vehicle 2 travels with the front and rear wheels 23
thereof, and transfers an article 3 loaded on the vehicle. The
transfer vehicle 2 is provided with a laser range finder (LRF) 21
fixed thereon for automatic (unmanned) operation. Herein, "fixed"
means that the mount position of the LRF 21 relative to the
transfer vehicle 2 is fixed.
[0023] The LRF 21 is for example mounted at a front portion (in the
direction of travel) of the transfer vehicle 2. The LRF 21 emits a
laser beam 22 and detects reflection light. That is, the laser beam
is reflected back from an object and detected. Thus an obstacle
located ahead in the direction of travel can be detected and thus a
collision with that object can be avoided. The transfer vehicle 2
may be additionally provided with a collision avoidance mechanism
or a mechanism for making an emergency stop upon detection of a
contact so that damage caused by an accident can be limited to a
minimum.
[0024] The laser beam 22 is emitted to a marker 1 placed ahead in
the direction of travel, and the reflection light therefrom is
detected by the LRF 21.
[0025] Since the transfer vehicle 2 travels on a flat floor surface
in general, it is expected that the loaded article 3 to be
transferred will not fall. However, in the case of an uneven floor
surface or wheels 23 having worn rubber, the loaded article 3 may
incline. Even at a small inclination of the order of 1 mm, the
article 3 may fall when it is a tall rack, for example. In
addition, even though the article 3 may not fall, a part of the
article 3 may be caught by a narrow transfer passage.
[0026] In the present embodiment, in order to transfer the article
3 in a stable manner, a marker 1 and an inclination detection
apparatus are provided as means to detect the inclination of the
transfer vehicle 2 in addition to the above described LRF 21.
[0027] The marker 1 has three marker rods Sa, Sb, and Sc to reflect
the laser beam 22 coming from the LRF 21 by three points. That is,
a point on a marker rod becomes a reflection point from which the
laser beam 22 is reflected. The marker 1 has a plate at a lower end
thereof to fix the positions of the three marker rods Sa, Sb, and
Sc.
[0028] In order to increase the reflection rate of the laser beam
22 reflected back from a marker rod to the LRF, each of the marker
rods is preferably covered by a retroreflective material having a
higher reflectance toward in a direction to the LRF 21 than
surrounding objects. Details of the three marker rods Sa, Sb, and
Sc, such as inclinations thereof, will be described later with
referring to FIG. 3 and subsequent FIGS. It is to be noted that the
number of the marker rods is not limited to three, but may be four
or more (i.e., the number of the reflection points may be four or
more), because the reflection points need only to be able to form
an inclination plane.
[0029] The marker 1 can be transferred and placed at a measurement
place in the vicinity of the transfer route of the transfer vehicle
2. The position and orientation of the marker 1 need not be
manually input as data in advance by an administrator nor
automatically input by measurement means using a global positioning
system (GPS) or the like. This makes it possible to flexibly change
the layout plan of a warehouse in which the article 3 to be
transferred is stored, thus increasing the flexibility of the
layout.
[0030] The three marker rods Sa, Sb, and Sc need to be placed in
such a manner that the three rods can be separately seen from the
LRF 21 because if some of the three rods are overlapped the number
of the reflection points becomes less than three. The marker 1 is
preferably placed in the vicinity of a location where the transfer
vehicle 2 is likely to incline, such as an uneven floor or an
inclined floor.
[0031] The inclination detection apparatus (not shown) computes the
inclination of the transfer vehicle 2 based on the positions of the
three reflection points, each of which is respectively measured by
the LRF 21 with respect to one of the three marker rods Sa, Sb, and
Sc. The inclination detection apparatus is a computing machine such
as a personal computer (PC) provided with a central processing unit
(CPU) and a memory, in which computing machine a process unit is
configured by the CPU loading program from storage means to the
memory and executing the program loaded.
[0032] When, for example, the inclination detection apparatus finds
three measurement objects in a specific range, the apparatus
recognize them as three marker rods Sa, Sb, and Sc.
[0033] The inclination detection apparatus may be, for example,
attached to the marker 1, mounted in the casing of the LRF 21,
mounted in the casing of the transfer vehicle 2, or installed in a
casing separated from them. That is, the inclination detection
apparatus may be in any configuration as long as the apparatus can
receive measurement data from the LRF 21.
[0034] FIG. 1B is a plan view of the transfer vehicle 2 as viewed
directly from the top thereof. In this plan view, an X axis
represents the direction of travel, and a Y axis represents a
sideward direction perpendicular to the X axis. The LRF 21 emits
(scans) a laser beam 22 with changing the angle thereof by a
predetermined increment (e.g., 5 degrees) in a predetermined range
relative to the forward front of the transfer vehicle 2 (e.g., in a
range of 270 degrees excluding vehicle rear). That is, the laser
beam 22 is emitted in an XY plane (two dimensional plane), thereby
allowing detection of the marker 1 situated in the vicinity of the
transfer vehicle 2.
[0035] FIG. 1C is a side view of the transfer vehicle 2 as viewed
directly from a side thereof. In this plan view, an X axis
represents the direction of travel, and a
[0036] Z axis represents a height direction. The LRF 21 emits the
laser beam 22 in the XY plane shown in FIG. 1B at a fixed
predetermined angle relative to the Z axis (in the figure, at an
angle of 0 degree, i.e., the horizontal direction). Note that, in
the following description, the positions on the three marker rods
Sa, Sb, and Sc at which the laser beam 22 is reflected are
respectively denoted by Pa, Pb, and Pc.
[0037] The plane containing Pa, Pb, and Pc (hereinafter referred to
as "inclination plane") represents the inclination of the transfer
vehicle 2 itself. For example, in FIG. 1C, the inclination plane is
parallel with the floor surface, indicating a state in which the
article 3 to be transferred is stable.
[0038] FIG. 2 is a flowchart showing a process of the transfer
vehicle 2 to travel, which process includes an inclination
detection process performed by the inclination detection apparatus.
Hereinafter, referring to FIG. 3 and subsequent figures as needed,
each of process steps will be described along with FIG. 2. At step
S11, when the transfer vehicle 2 recognizes a travel destination
based on an input from a user or the like, the transfer vehicle 2
activates the LRF 21 and makes the LRF 21 start emission of a laser
beam 22.
[0039] At step S12, the transfer vehicle 2 sets a travel route from
the current position to the travel destination, for example
according to the result of a route search performed by a navigation
system.
[0040] In the travel process of the transfer vehicle 2 on the
travel route, which will be described below, the transfer vehicle 2
may or may not have loaded the article 3 to be transferred. That
means execution of processes for detecting an inclination of the
transfer vehicle 2 and for correcting the inclination is not
limited to when the article 3 has been loaded.
[0041] At step S21, the LRF 21 determines whether a marker 1 in the
vicinity of the LRF 21 is found by reflection of a laser beam
emitted from the LRF 21 from the current position. If YES at step
S21, the flow proceeds to step S31; if NO, the flow proceeds to
step S22.
[0042] At step S22, the transfer vehicle 2 travels toward the
travel destination recognized in step S11 along the travel route
set in step S12. Optionally, the transfer vehicle 2 may be
configured to, when a marker 1 is found in step S21, change the
route set in step S 12 in consideration of the width of the vehicle
including the article 3 based on the inclination of the vehicle. A
route change during travel can be carried out by comparing the
measured distance data of the surroundings obtained by the LRF 21
with map data embedded in the transfer vehicle 2.
[0043] At step S23, the transfer vehicle 2 determines, after the
transfer vehicle 2 has traveled a predetermined distance or after a
predetermined period of time has elapsed, whether the transfer
vehicle 2 has reached the travel destination. If the travel
destination has been reached (YES at step S23), the travel process
is terminated, otherwise (NO at step S23) the process returns to
step S21.
[0044] If Yes at step S21, the inclination detection apparatus uses
the detection of the marker 1 as a trigger signal of special
operations. During the time in which the marker 1 is being
detected, the inclination detection apparatus continue measuring
the inclination of the vehicle body (steps S31 to S33 described
below) and making an adjustment to keep the loaded article in a
level position (steps S34 and S35 described below) while the
transfer vehicle travels. Hereinafter, details of each of the
process steps (steps S31 to S35) of the inclination detection
apparatus will be described.
[0045] At step S31, the inclination detection apparatus obtains the
positions of the three reflection points of the marker 1 and the
length of the sides of the triangle formed by the reflection points
as described below.
[0046] FIG. 3A is an explanatory diagram for explaining a process
of detecting the reflection points Pa, Pb, and Pc relative to the
LRF 21. Hereinafter, although the detection process will be
described with a focus on the reflection point Pa, the other
reflection points Pb and Pc can be detected by the same processing
as well.
[0047] The laser beam 22 emitted from the LRF 21 is reflected at
the reflection point Pa on the marker rod Sa, and the reflection
light of the laser beam returns to the LRF 21.
[0048] Therefore, a reflection point distance La, which is the
distance from LRF 21 to the reflection point Pa, can be computed
from the time for the laser beam to reach the reflection point Pa
and be reflected back to LRF 21 (i.e., reflection light arrival
time--laser beam emission time). In addition, the emission angle
.theta.a of the laser beam is predetermined at the time of
emission. That is, the position of the reflection point Pa can be
obtained as a combination of the distance La to the reflection
point and the emission angle .theta.a.
[0049] FIG. 3B is an explanatory diagram for explaining a process
of forming a triangle from the positions (sets of a distance to
reflection point and an emission angle .theta.) of the reflection
points detected in the process explained with FIG. 3A and obtaining
each length of the sides Lab, Lac, and Lbc of the triangle.
[0050] Positions of the reflection points are each represented in a
polar coordinate system (distance to reflection point, emission
angle .theta.), and a triangle whose three vertexes correspond to
the three reflection points is formed. The sides of the triangle
are respectively denoted La, Lbc, and Lac. Herein, the side
connecting the reflection points Pa and Pb is denoted Lab,
indicating "a" and "b" in subscripts.
[0051] At Step S32, the inclination detection apparatus obtains
positions of the reflection points in the marker based on the
lengths of the sides of the triangle obtained in the process
explained with FIG. 3B.
[0052] FIG. 3C is an explanatory diagram showing that an
inclination plane is obtained by determining points on marker rods
Sa, Sb, and Sc of the marker 1 which form a triangle having the
same lengths of sides as the lengths of the sides Lab, Lac, and Lbc
obtained in the process explained in FIG. 3B.
[0053] The three marker rods Sa, Sb, and Sc are disposed in such a
manner as to have different inclinations with respect to one
another. The three marker rods Sa, Sb, and Sc are for example fixed
in a skewed fashion with respect to one another (i.e., they are not
in the same plane), and their respective inclination orientations
and positional relation with respect to at least one point are
known.
[0054] Based on such condition of the three marker rods Sa, Sb, and
Sc, when one arbitrary point is selected from each of the marker
rods (for example, point Pa is selected from the marker rod Sa), a
triangle connecting the positions of the three selected points on
the marker rods is formed and the lengths of the three sides the
triangle are uniquely obtained.
[0055] In other words, when those lengths of the sides of that
triangle is given, it is possible to uniquely identify the
positions of the three selected points on the marker rods because
the three marker rods Sa, Sb, and Sc have different inclinations
with respect to one another and their inclinations and positional
relation are known. As a result, it is possible to obtain the three
dimensional positions of the three points.
[0056] Herein, the points of contact of the plate with the marker
rods are denoted Oa, Ob, and Oc, each of which is represented by
coordinates relative to Oc. That is, Oc is defined as an
origin.
[0057] The marker rod Sc originates from the contact point Oc (0,
0, 0) and extends in the direction of the normal vector (0, 0, 1).
That is, the marker rod Sc extends perpendicular to the plate.
[0058] The marker rod Sb extends from the contact point Ob (xb0,
yb0, 0) in the direction of a vector (.alpha.b, .beta.b, .gamma.b).
The marker rod Sa extends from the contact point Oa (xa0, ya0, 0)
in the direction of a vector (.alpha.a, .beta.a, .gamma.a).
[0059] For a point Pa(xa, ya, za) on the marker rod Sa, a point
Pb(xb, yb, zb) on the marker rod Sb, and a point Pc(0, 0, zc) on
the marker rod Sc, the following equations hold:
(xb-xb0)/ab=(yb-yb0)/.beta.b=zb/.gamma.b
(xa-xa0)/a.alpha.=(ya-ya0)/.beta.a=za/.gamma.a
[0060] Thus, positions of Pa and Pb are given as follows:
Pb=(.alpha.b.times.xb/.gamma.b+xb0, .beta.b.times.zb/.gamma.b+yb0,
zb)
Pa=(.alpha.a.times.za/.gamma.a+xa0, .beta.a.times.za/.gamma.a+ya0,
za)
[0061] The inclination detection apparatus determines the positions
of the reflection points Pa, Pb, and Pc in the coordinate system
relative to the origin Oc so that the combination of the lengths of
the sides of the triangle obtained in the process explained with
FIG. 3B matches with the combination of the lengths of the sides of
a triangle formed by the above expressed points Pa, Pb, and Pc
(i.e., translates the positional relation represented by the
lengths of the sides of a triangle to relative positions on the
marker rods). This makes it possible to obtain the positions of the
reflection points in the marker 1 at step S32.
[0062] For example, when the inclination detection apparatus
obtains a combination of lengths of the sides of the triangle as 30
cm, 50 cm, and 60 cm, the apparatus can uniquely identify positions
of the reflection points Pa, Pb, and PC which form a triangle
having the same combination of lengths of sides as that combination
on the marker rods Sa, Sb, and Sc.
[0063] The translation into the relative coordinate system means,
in other words, to determine a set of three points Pa, Pb, and Pc
which at the same time satisfy: a constraint that the triangle
formed by the three points have the same combination of lengths as
those of the triangle derived from the reflection points, the
positions of which are represented in the polar coordinate system
(distance L to reflection point, emission angle .theta.); and a
constraint that the three points be respectively on the marker rods
(each of the three points be on an extended line on a predetermined
inclined vector extending from a point of contact O), where the
rods are fixed in advance and points on the rods are represented in
a relative coordinate system established by the marker rods.
[0064] Thus, calculation parameters (points of contact, vectors)
for determining points on the three marker rods Sa, Sb, and Sc in
the relative coordinate system are to be input to the inclination
detection apparatus in advance by an administrator of the warehouse
or the like.
[0065] At step S33, the inclination detection apparatus obtains an
inclination plane from the positions of the reflection points Pa,
Pb, and Pc which have been found in the marker in step S32. In
other words, the inclination detection apparatus identifies the
plane including the three reflection points in space coordinates as
the inclination plane.
[0066] At step S34, the inclination detection apparatus determines
whether the inclination plane obtained in step S33 is level. FIG.
4A shows a case in which the transfer vehicle 2 has an inclination
with a front portion of the transfer vehicle 2 being raised (bends
oneself back), where the inclination plane is formed such that the
plane has an upward inclination in the travel direction of the
vehicle (i.e., the vehicle looks up). Since the LRF 21 is fixed on
the transfer vehicle 2, the inclination of the transfer vehicle 2
can be obtained based on the inclination of the inclination plane.
That is, the angle between the inclination plane and the plate of
the marker 1 (i.e., the level plane) corresponds to the angle of
the inclination of the transfer vehicle 2 with respect to the floor
surface (i.e., inclination of vehicle).
[0067] In contrast, FIG. 4B shows a case in which the transfer
vehicle 2 has an inclination with the front portion of the transfer
vehicle 2 being lowered (bends oneself forward), where the
inclination plane is formed such that the plane has a downward
inclination in the travel direction of the vehicle (i.e., the
vehicle looks down).
[0068] As another example, FIG. 4C shows a case in which the
transfer vehicle 2 has an inclination with the front portion of the
vehicle being raised when going up a slope, where the inclination
plane is formed such that the vehicle looks up like the case of
FIG. 4A.
[0069] The cases illustrated in FIGS. 4A, 4B, and 4C are each a
case in which the inclination plane is not level and therefore the
determination at step S34 is negative (No).
[0070] In FIG. 1C, the plate of the marker 1 is placed level,
whereas in FIG. 4C, the plate is placed in an inclined manner
(along the inclination of the slope). These cases are supported by
using different sets of the parameters for obtaining the reflection
points Pa, Pb, and PC (i.e., parameters consisting of contact
points Oa, Ob, and Oc, and vectors representing the orientations of
the marker rods), even though the marker 1 of FIG. 1C and the
marker 1 of FIG. 4C are the same structure. For example, the marker
rod Sc extends vertically along the normal vector (0, 0, 1) when
the marker plate is placed level, and the marker rod Sc extends in
a direction not perpendicular to a horizontal plane when the marker
plate is placed in an inclined manner.
[0071] It is noted that FIGS. 4A to 4C show examples in which the
inclination plane is not level only in the direction of the X axis.
However, this is merely for ease of visual understanding purposes.
The inclination detection apparatus is capable of detecting an
inclination in the direction of the Y-axis as well.
[0072] Since the laser beam 22 scans the XY plane as indicated in
FIG. 1B, it is possible to detect a plane inclined in the direction
of the Y-axis (for example when the front and rear wheels 23 on the
right side are lowered relative to the wheels on the left side) as
well as a plane inclined in both the X-axis and Y-axis directions
(for example when only the front right wheel 23 is lowered relative
to the other wheels 23).
[0073] The inclination detection apparatus is able to obtain the
amount of sinking of the transfer vehicle 2 in addition to the
inclination of the transfer vehicle 2. The sinking here means that
the transfer vehicle 2 is lowered as a whole by a predetermined
height (amount of sinking), for example, due to an excessive heavy
load of an article 3 to be transferred, with the transfer vehicle 2
being kept level.
[0074] As described in the description of step S32, the inclination
detection apparatus is able to obtain each of the positions of the
reflection points in marker 1 as space coordinates, thus the
apparatus is also able to derive the amount of sinking of the
transfer vehicle 2 by comparing the height of the inclination plane
relative to the floor surface (the plate of the marker 1) with the
height of the emission of the laser beam 22 (height in the Z-axis).
Based on the information of the obtained amount of sinking, the
inclination detection apparatus may utilize the information for
example to warn an overloading of the article 3 when the sinking
amount is greater than a predetermined threshold value.
[0075] At step S35, the inclination detection apparatus recognizes
an abnormal condition when the inclination plane is not level, and
corrects the inclination of the article 3 to a level position.
Hereinafter the correction methods illustrated in FIGS. 5A to 5D
will be described.
[0076] FIG. 5A is a plan view illustrating an inclined transfer
vehicle with an article 3 loaded on a loading platform 24 of the
vehicle. FIG. 5B is a plan view illustrating that the article 3 has
been restored to its level position by adjusting the loading
platform 24.
[0077] Assume that the inclination plane (i.e., loading platform
24) obtained in step S33 has an inclination with a rear portion of
the inclination plane in the direction of travel being lowered. The
article 3 loaded on the loading platform 24 in this state may fall
backward.
[0078] Thus, the inclination detection apparatus sends to an
elevating mechanism 24a for raising and lowering the loading
platform 24 a control signal commanding the mechanism to change the
inclination of the loading platform 24, in such a manner as to
restore the inclination of the inclination plane to a level
position. As a result, the transfer vehicle 2 remains inclined but
the article 3 on the loading platform 24 becomes level and
stabilized.
[0079] FIG. 5C is a plan view illustrating an inclined transfer
vehicle 2 provided with actuators between the vehicle body and
wheel shafts. FIG. 5D is a plan view illustrating that the whole of
the transfer vehicle 2 has been restored to its level position by
adjusting the actuators.
[0080] The wheels 23 are provided with actuators 23a for front
wheels and actuators 23b for rear wheels. These actuators are each
provided between the vehicle body and a wheel shaft, and can be
operated so as to modify the inclination of the vehicle body by the
actuator pressing the wheel shaft. The actuators are provided with
a screw or worm gear mechanism so as to maintain the posture of the
vehicle even while power is off.
[0081] Assume that the inclination plane (i.e., loading platform
24) obtained in step S33 has an inclination with a rear portion of
the inclination plane in the direction of travel being lowered. The
inclination detection apparatus corrects the inclination of the
vehicle body by driving the actuators so that the heights of the
front wheels become level with those of the rear wheels. As a
result, the transfer vehicle 2 becomes level, and thus the loaded
article 3 also becomes level and stabilized.
[0082] FIG. 6A is a perspective view illustrating an embodiment of
the invention which is different from the embodiment illustrated in
FIG. 1A. The transfer vehicle 2 is provided thereon with a loading
platform 24, on which an article 3 to be transferred is to be
loaded and which is structured as a rotatable stage capable of
changing the inclination angle thereof. An article 3 broader than
the vehicle width may collide with a narrow passage. A tall article
3 may fall down even with a small inclination thereof due to a high
center of gravity. So the inclination detection apparatus controls
(rotates) the rotatable stage to restore the inclination thereof to
its level position, thus preventing a collision or a fall of the
article 3.
[0083] The marker 1 is not limited to be placed on the same height
as the floor surface on which the transfer vehicle 2 travels. It
may be, for example, placed on a pedestal the upper surface of
which is parallel to the floor surface.
[0084] FIG. 6B is a perspective view illustrating embodiments of
the marker 1 which are different from the embodiment illustrated in
FIG. 1A. The three marker rods Sa, Sb, and Sc are not limited to be
skewed. They may be structured to intersect at a point in a space,
provided that inclinations of the three rods Sa, Sb, and Sc are
different with respect to one another. The marker 1b is an example
in which the marker rods intersect at the bottom plate. By this
structure, the marker 1b may have a small amount of an occupied
volume, which permits the marker 1b to be readily transferred. The
marker 1c is an example in which the marker rods intersect at a top
portion thereof. By this structure, with the three marker rods Sa,
Sb, and Sc being stabilized in a space by the same principle as the
tripod for a camera, the bottom plate of the marker can be
eliminated and thus the occupied area can be reduced.
[0085] Further, instead of the marker 1c having an intersection at
the top portion thereof, the marker 1c may be structured such that
the marker rods in the vicinity of the intersection are
omitted.
[0086] In the above described embodiments of the invention, the
inclination detection apparatus uses, when detecting the
inclination of the transfer vehicle 2 on which the article 3 to be
transferred has been loaded, the information obtained from the
laser beam 22 emitted from the LRF 21 of the transfer vehicle 2 to
the marker 1. The marker 1 is composed of three marker rods Sa, Sb,
and Sc, the inclinations of which are different with respect to one
another, and an inclination plane representing the inclination of
the transfer vehicle 2 is uniquely obtained based on three
reflection points of the laser beam 22.
[0087] As described above, the inclination detection apparatus in
combination with the marker 1 and the LRF 21 is able to restore a
loaded article 3 to a level position. Therefore, it is possible to
prevent the article 3 from falling from the transfer vehicle 2 and
prevent a collision of the article 3 protruding from the transfer
vehicle 2 with a passage. Further, since it is possible to expect
that the article 3 do not protrude from the transfer vehicle 2, the
transfer route of the transfer vehicle 2 can be narrowed insofar as
it is possible to transfer the article 3, thereby improving the
storage efficiency of the warehouse.
[0088] Since the LRF 21 is able to autonomously find a maker 1
existing therearound by emitting a laser beam 22, it is possible to
eliminate time and effort of an administrator to input the position
of the marker 1 in the warehouse in advance. Therefore, when making
changes in the layout of the warehouse, the marker 1 may be merely
hand-carried as is to change its position.
[0089] The present invention is not limited to the above described
embodiments, but includes various variations. For example, the
above-described embodiments have only been described in detail for
a better understanding of the invention and are therefore not
necessarily limited to a configuration containing all the described
constituent elements.
[0090] In addition, part of the configuration of a certain
embodiment may be replaced with the configuration of another
embodiment, and the configuration of a certain embodiment may be
modified by adding a configuration of another embodiment.
[0091] Further, a portion of the configuration in each of the
embodiments may be modified by adding other configuration, by
deletion, or by replacing with other configuration. Furthermore,
the above-described configurations, functions, processing portions,
processing means, and so on may be realized in hardware by
designing some or all of them, for example, using an integrated
circuit.
[0092] Additionally, the above-described configurations, functions,
and so on may be realized by software such that a CPU interprets
programs that achieve respective functions.
[0093] Information such as programs, tables, and files for
realizing the individual functions may be stored in a storage
device such as memory, a hard disk, or a solid state drive (SSD),
or a recording medium such as an integrated circuit (IC) card, a
secure digital (SD) card, and a digital versatile disc (DVD).
[0094] In addition, the control lines and information lines
represent those that are considered to be necessary for description
purposes, and do not necessarily represent all the control lines
and information lines that are necessary for a product. In
practice, almost all structures may be considered to be mutually
connected.
REFERENCE SIGNS LIST
[0095] 1 Marker (equipment for inclination detection) [0096] 2
Transfer vehicle (Mobile body) [0097] 3 Article to be transferred
[0098] 21 Laser range finder (LRF) [0099] 22 Laser beam [0100] 23
Wheels [0101] 24 Loading platform [0102] 24a Elevating mechanism
for raising and lowering loading platform [0103] 23a Actuators for
front wheels [0104] 23b Actuators for rear wheels [0105] Pa, Pb, Pc
Reflection points [0106] Sa, Sb, Sc Marker rods
* * * * *